Fix typing non-English characters using an input method (key composing) in the author/tags/etc fields in the metadata dialog not working. Fixes #1266795 [Character composing doesn't work on metadata editor](https://bugs.launchpad.net/calibre/+bug/1266795)
Slightly more useful error on checkpoint stack corruption
Use QInputMethodEvent to make charmap work with all widgets
Fix handling of non-BMP characters on narrow builds of python (windows).
Also show busy cursor while searching.